Power Supplies

Automatic Water Refiller for Air-Coolers Schematic Circuit Diagram

Air coolers function by introducing moisture into the air to provide cooling in a room. An exhaust fan or blower then circulates this moistened air inside the room, resulting in a decrease in room temperature. However, these coolers necessitate regular water refilling. Here, we present a circuit designed to automatically refill water in an air cooler tank whenever the water level falls below a predefined threshold.

Circuit and working

The circuit diagram for the automatic refiller water system for air coolers is presented in Figure 1. This system is constructed around components such as the NE555 timer (IC1), transistor BC547 (T1), reed switches (S1 and S2), and several other components. IC1 is configured in a manner akin to the bistable mode, with the sole distinction being the connection of switch S1 to pin 6 instead of pin 4.

Automatic Water Refiller for Air-Coolers Schematic Circuit Diagram 1

Fig. 1

The two reed switches (S1 and S2) are affixed at upper and bottom levels of the tank as shown in Fig. 2. Working of the circuit is pretty simple.

Automatic Water Refiller for Air-Coolers Schematic Circuit Diagram 2

Fig. 2

In the event that the water level falls below the established threshold, the magnetic float causes reed switch S2 to close, grounding pin 2 of IC1. Consequently, the voltage at pin 2 drops below 1/3 of Vcc, causing the output of IC1 to go high. This activation triggers the relay, which in turn energizes the solenoid valve. As a result, water begins to flow into the tank.

Once the tank reaches its full capacity, the magnetic float closes reed switch S1. This action causes pin 6 of IC1 to rise above 2/3 of Vcc, causing the output to go low. Consequently, the relay is de-energized, leading to the deactivation of the solenoid valve, thereby halting the flow of water into the cooler tank.

Construction and testing

An actual-size PCB layout of the automatic water refiller for air-coolers is shown in Fig. 3 and its components layout in Fig. 4. Assemble the circuit and enclose it in a suitable cabinet.

Automatic Water Refiller for Air-Coolers Schematic Circuit Diagram 3

Fig. 3

Schematic Circuit Diagram 4

Fig. 4

To implement a water level sensing system for the air cooler’s water tank, follow these steps:

  1. Connect a narrow PVC pipe to the water tank, as shown in Figure 2, positioning it between the drain outlet and the overflow outlet.
  2. Place a magnetic float inside the PVC pipe. Ensure that the magnetic float is crafted using a small speaker magnet and a hollow float ball. The diameter of the magnetic float should be slightly smaller than that of the PVC pipe, allowing it to move freely either from the bottom to the top or vice versa depending on the water level.
  3. Install one reed switch on the pipe near the drain outlet and another reed switch near the overflow outlet.
  4. If feasible, insert the pipe into the inner wall of the tank with the reed switches attached externally.

Schematic Circuit Diagram 5


If the load is a 12V solenoid valve as shown in Fig. 5, use 12V DC supply to power the circuit and the load. Alternatively, use 230V AC supply at CON3 and external 12V adaptor at CON1, if the load is a 230V centrifugal pump.

Schematic Circuit Diagram 6


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